In western Micronesia archaeological sites containing material-culture remains spanning millennia are rare. This paper reports one from Ulong Island in Palau, which is radiocarbon dated to 3000 cal. B.P. The pottery sequence was divided into three assemblages, each distinguished by distinct vessel forms and by the type and proportion of nonplastic temper inclusions. An abrupt transformation of the ceramic assemblage is tentatively dated to around 2400 cal. B.P., coincident with substantial landscape alteration on the main island where pottery was manufactured, indicating that anthropogenic activity may have constrained the raw materials available to prehistoric potters. There is a discontinuity in the sequence from 2000-1000 B.P. that might represent an hiatus in site use. Critical consideration of paleoenvironmental data pointing to human arrival at 4500-4300 cal. B.P. suggests, instead, that climatic events may be responsible for the observed palaeoecological changes. If so, then sites dating to 3300-3000 cal. B.P., such as Ulong, could well be among the oldest in western Micronesia. KEYWORDS: archaeology, Palau, colonization, culture sequence, western Micronesia.